It is known in the art of electrical machines, and particularly in the field of electrical generators and motors, that the use of energized electrical coil windings and non-energized iron magnetic core elements in relatively close proximity to each other as components of an electrical coil assembly gives rise to the risk of electric faults, such as faults between the coil windings and the iron magnetic core or faults between the turns or layers within the coil windings. Consequently, it is known that an effective method for protecting the coil windings and the magnetic core from faults is critical to reducing the risk of such electric faults, and therefore the use of conventional electrical insulating or dielectric materials on one or both of the coil windings and magnetic core is well established in electrical generators, motors and other electrical machines according to the prior art. In one such conventional design for an electrical generator or motor for use in dry service, a resin or enamel dielectric material is applied to the magnetic core, and an enamel dielectric material is applied to the magnetic wire of the coil windings in order to reduce the risk of electrical faults between the coil windings and magnetic core, or within the coil windings.
It is also known to use electrical cable for the coil windings in an electrical machine, such as a generator or motor, to provide insulation between the coil windings and magnetic core, and within the coil windings. The use of electrical cable for coil windings to allow high voltage operation of the coil windings has been shown in the electrical generators of U.S. Pat. No. 6,927,505 to Leijon et al., and U.S. Pat. No. 7,019,429 to Larsson et al., for example, which disclose the use of electrical cable comprising layers of polyethylene and semiconductor dielectric insulation for the generator coil windings.
The risk of electric fault in an electrical machine such as a generator or motor is substantially increased upon exposure of the coil windings and magnetic core to a conductive and/or chemically aggressive environment such as seawater. It is well understood that the small size of water molecules and their interaction with the electrical field around the energized coil windings create a significant challenge in preventing the electrical breakdown of many known types and combinations of dielectric insulation materials in an operating environment with exposure to seawater. The coupled electrochemical and dielectric stresses in such an operating environment lead to premature aging and electrical breakdown of dielectric insulation materials used in conjunction with both magnetic core and coil windings of conventional electrical machines, and can ultimately lead to faults and premature failure of the coil assembly.
In particular, known design approaches for providing protection against electrical coil assembly faults in electric machines subject to frequent wetting, spray and/or immersion (total or partial) in an electrically conductive and/or chemically aggressive environment, such as seawater or chemical solution, are limited in their effectiveness. Existing design approaches for protection of electrical machines in immersion service have included:                use of a liquid insulation medium, such as oil, as a barrier between the conductive environment and the electrical coil assembly, resulting in differential pressures between the liquid insulation medium and surrounding environment and requiring reliance on seals to contain the liquid insulation medium, which are susceptible to breakdown and leakage over prolonged immersion use, and risks the release of the liquid insulation medium and failure of the electrical coil assembly should such seals leak, or should the liquid insulation material degrade over time; and        isolation of the entire electrical machine or at least a portion including the electrical coil assembly in a watertight compartment utilizing mature sealing technology, which remains potentially susceptible to leakage of such seals and accompanying risk of electrical coil assembly failure over prolonged immersion use and may be impractical in many applications due to the bulk and complexity of a watertight enclosure, and the regular maintenance required by many sealing technologies.        